The invention is related to a method of writing a pattern on a media and a data storage device, particularly, control of timing in writing a pattern on a rotating media.
A device using various kinds of medium such as an optical disk and a magnetic tape as a data storage device is known. Among such devices, a hard disk drive (HDD) is widely used as a storage device of a computer and is an essential device in a current computer system. Furthermore, the excellent characteristics of HDD have increased the area of the usage of the HDD not only in a computer system but also in a removable memory used in a moving picture image recording/playing device, a car navigation system, a cellular phone, a digital camera or the like.
A magnetic disk used in an HDD has plural tracks formed into the shape of concentric circles. In the respective tracks, both servo data and user data are written. Accessing to a desired area (address) by a head device fabricated by a thin-film process in accordance with the servo data enables data writing or data reading to be performed. In the data reading process, a signal read from the magnetic disk by means of the head device undergoes a signal process such as waveform shaping or decoding in a signal processing circuit to be sent to a host. Data transmitted from the host similarly undergo a process in a signal processing circuit, and then, written in the magnetic disk.
As described above, the respective tracks comprise a user data area for storing the user data and a servo pattern area for storing the servo data. The servo pattern (referred to as a product servo pattern in this disclosure) comprises a cylinder ID, a sector number, a burst pattern and the like. The cylinder ID indicates an address of a track. The sector number indicates a sector address in a track. The burst pattern includes relative location information of a magnetic head to a track.
The product servo pattern consists of plural sectors separated in a circumferential direction in the respective tracks. Locations (phases) of the product servo pattern in the respective sectors coincide with each other in the circumferential direction over the whole tracks. Data are read from or written on the magnetic disk during rotation of the magnetic disk, confirming a location of the magnetic head on the basis of the servo data.
The product servo pattern is written on a magnetic disk in a factory before shipping of an HDD as a product. Conventionally, the product servo pattern has been typically written by means of a servo writer, which is an external device. An HDD is set in the servo writer, which positions a head in the HDD by means of a positioner (an external positioning mechanism), to write a product servo pattern generated in a product servo pattern generation circuit on a magnetic disk.
The cost of STW (servo track write) occupies a significant portion in the present manufacturing process of HDD. Recently, there has been a keen competition in HDD technologies to achieve high density, which causes an increase in TPI (track per inch), which results in the increase in the number of tracks and the reduction of the width of tracks (a track pitch). This causes significant increase in STW time and in precision of a servo writer, and thereby, in the cost of STW. In order to reduce the cost of STW, reduction of cost of the servo writer and STW time is extremely important.
In this context, SSW (self servo write) has been proposed as a new method to write servo patterns. The SSW is different from the conventional STW in that only a mechanism part of a main body of an HDD is used and a spindle motor (SPM) and a voice coil motor (VCM) in the HDD are controlled by means of an external circuit to write a product servo pattern by means of the external circuit. This contributes to the reduction in cost of a servo writer.
As a method of SSW, known is a method in which a pattern having been written on an inner radial side or an outer radial side is read by means of a read device to perform positioning of the head, taking advantage of a difference in location in a radial direction between the read device and a write device of the head device (refereed to as a read/write offset), while a new pattern is written on a desired track provided separately by the read/write offset by means of the write device.
In the SSW, locations of the respective product servo patterns should precisely coincide with the adjacent servo tracks in the circumferential direction. Because the product servo patterns are written so as to be partially overlapped between the adjacent servo tracks, signals from the adjacently written patterns are not well superimposed in the case where the phases in the circumferential direction do not coincide with each other, which results in problems such as reduction in the read amplitude of the pattern. Further, in view of simplicity of the control, the respective patterns are preferably written in the circumferential direction at even intervals.
Accordingly, in the SSW, precise control of locations in the circumferential direction, that is, timing for writing is required in writing a product servo pattern or another pattern, which is a reference to the product servo pattern. There has been a known technology in which the intervals between written patterns are used for correcting timing for writing in order to control intervals of patterns in a circumferential direction in propagation of a timing pattern in self servo writing. See, e.g., JP-A-8-212733.